Aircraft designers and manufacturers are under continual pressure to reduce the aerodynamic drag on aircraft surfaces, so as to increase aircraft performance and/or reduce aircraft fuel consumption. A significant amount of aircraft drag is caused by boundary layers that build up on the exposed surfaces of the aircraft during flight. A boundary layer is a thin film of low velocity, low dynamic pressure air located near a solid boundary and resulting from the air being at rest at the interface with the solid boundary. The boundary layer build-up on the aircraft wings and/or other external surfaces causes skin friction and therefore significantly contributes to airplane drag. Because laminar boundary layers create less friction at the aircraft surfaces than do turbulent boundary layers, one technique for reducing aircraft drag is to establish and preserve a laminar boundary layer over a significant portion of the aircraft external surfaces.
One effective method for establishing and preserving a laminar boundary layer is to remove a small amount of the boundary layer flow through the exposed flow surface via a distributed suction system. A representative system in accordance with the prior art is shown in FIG. 1. Such a system 40 installed on a wing 20 includes perforations 46 in an external surface 43 of the wing 20. The external surface 43 can have various regions with different porosities. Individual ducts 48 incorporating flow control valves 49 collect the flow removed from the various regions of the external surface 43 and provide the flow to a collection duct 71. A compressor 70 (e.g., a turbo-compressor or electric motor driven compressor) generates the suction force required to draw the boundary layer air through the perforations 46 and discharge the air overboard the aircraft.
In order to establish and control the desired suction distribution over the external surface 43, the suction system 40 includes multiple, sub-surface compartments with corresponding flow ducts 48 and associated individual control valves 49. While such a system has produced an extended region of laminar flow over the external surface 43, the weight, complexity and power requirements of the system detract from the potential economic benefit that it can provide.